Classification Of Oxides

This topic educates with the classification of oxides based on the nature and properties of compounds. Oxides are binary compounds formed by the reaction of oxygen with other elements. Oxygen is highly reactive in nature. They react with metals and non-metals to form oxides.

What are Oxides?

The classification of oxides is done into neutral, amphoteric and basic or acidic based on their acid-base characteristics.

1. An acidic oxide is an oxide that when combined with water gives off an acid.
2. A basic oxide is an oxide that when combined with water gives off a base.
3. When a substance reacts chemically, both as a base or acid is termed as amphoteric oxide.
4. Neutral Oxide is one that neither has an acidic characteristic nor a basic one.

Metal Oxides have an oxidation number of -2 and generally comprise an oxygen anion. The Earth’s crust is mostly made up of oxides that are solid. Oxide coatings can get formed over pure elements too, for instance, a foil made of aluminium gets covered by a thin skin of Al₂O₃, and this skin defends the rest of the foil from corrosion.

Also read:

• Amphoteric Oxides

Classification Of Oxides

Depending upon nature and the properties exhibited by compounds, they are classified into

• Acidic oxides
• Basic oxides
• Amphoteric oxides
• Neutral oxides

Basic oxide:

Metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. Group 1, 2 and lanthanides form basic compounds of oxygen when they react with dioxygen. During the formation of these compounds, a large amount of energy is released. These compounds readily react with water except for a few exceptions.

Examples: M₂O₃, MO₂, ThO₂

Na₂O + H₂O → 2NaOH

Acidic oxide:

Non-metals react with oxygen to form acidic compounds of oxides which are held together by covalent bonds. These compounds can also be called acid anhydrides. Acid anhydrides usually have a low melting and boiling point except for compounds like B₂O₃ and SiO₂ which have high melting points and form giant molecules.

Examples: NO, CO₂

SO₃ + H₂O → H₂SO₄

B₂O₃ + H₂O → 2H₃BO₃

Amphoteric oxide:

Amphoteric oxides are compounds of oxygen which exhibit both acidic as well as basic characteristics. These oxides when reacting with acid undergo a neutralization reaction to form water and salt. This exhibits the basic property of the compounds. Similarly amphoteric oxides reacts with the alkali to form salt and water, exhibiting acidic properties. Example: aluminium oxide

Acidic characteristics:

Al₂O₃ + 6HCl → 2Al₃⁺ + 6Cl^– + 3H₂O

Basic characteristics:

Al₂O₃ +2OH^– + 3H₂O → 2[Al (OH)₄]^–

Neutral Oxides:

Some compounds react with oxygen to form oxides which do not exhibit acidic nor basic characteristics. Such compounds are called neutral compounds of oxygen.

Example: NO, CO.

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